1. Field of the Invention
This invention relates to self-contained systems for dispensing a liquid such as water. More particularly, this invention relates to self-contained fire extinguishing systems.
2. Description of the Prior Art
Self-contained automatic sprinkler systems are known in the art. Such systems are supplied by a water tank, and are suitable for protecting a limited area from fire. The more familiar automatic sprinkler systems, in contrast, are generally supplied from a water main and typically protect a whole building or a section or wing thereof. Self-contained systems are much more easily installed than conventional systems in existing buildings.
Various self-contained automatic sprinkler systems are described in "Fire Protection Handbook", 12th Edition, 1962, George H. Tryon, ed., National Fire Protection Association, Boston, Mass., publisher, pages 16-220 to 16-225. Particular attention is directed to page 16-224, where an apparatus, comprising a water tank which is not continuously pressurized, cylinders containing compressed gas (nitrogen) for pressurizing the water tank on command, and a manifold system which includes a pressure reducing and regulating valve, is described. Disadvantages of such a system are that it requires storage of a compressed gas under high pressure (on the order of 2,000 psig), that the pressure reducing valve may not operate properly after long standing and that the compressed gas cylinders may gradually lose pressure due to leakage through the reducing valve or an actuating valve. Since the apparatus is an emergency action device, it may stand in "ready" or unactuated state for years before being called on to perform. Periodic inspection is highly desirable to make sure that the system is in good working order.
Use of a volatile liquid under pressure is known in the beverage dispensing and in the aerosol dispenser arts, although not (as far as applicant is aware) in the art of sprinkler systems for fire protection. The references discussed below illustrate systems in which a volatile liquid under pressure supplies the pressure necessary for dispensing a liquid.
U.S. Pat. No. 3,613,954 to Bayne describes a carbonated beverage dispenser which includes a first container in which a carbonated beverage (e.g., beer) is stored under pressure and at sub-atmospheric temperature, a spigot which controls the dispensing of the beverage, and a second container for a volatile liquid (or liquefied gas), such as a fluorocarbon, in liquid form under pressure. As the beverage is dispensed, a portion of the volatile liquid in vapor form flows from the second container to the head space of the first container to maintain pressure in the first container. In the embodiments of FIGS. 1-6, the composition of the liquefied gas is such that its vapor pressure at 45.degree. F. (7.degree. C., which is the preferred beer storage temperature) will be about 15-20 psig (approximately 2-2.3 atmospheres absolute), which is the desired headspace pressure in the first container. Also, in the preferred embodiment, the container for liquefied gas is outside the first container so that the heat of vaporization will be supplied from the surroundings rather than from the contents of the first container. FIGS. 7 and 8 illustrate embodiments in which a more volatile liquefied gas, i.e., one having a vapor pressure considerably higher than 15-20 psig at 45.degree. F., is used. The container for liquefied gas in these embodiments is below the normal liquid level inside the first container.
U.S. Pat. No. 2,976,897 to Beckworth describes a reusable pressurized canister containing a liquid to be dispensed and pressurized by a pressure reservoir.
U.S. Pat. No. 3,815,793 to Morane et al. describes an aerosol container which is pressurized by a volatile liquid (or a liquefied gas) stored under pressure in a cartridge which is inside the principal container. The contents of the aerosol container are pressurized at all times.
U.S. Pat. No. 3,523,583 to Poitras et al. shows a fire extinguishing apparatus comprising a cylinder filled with a fire extinguishing fluid and having an expandable end wall at one end, a frangible end wall at the other end, and a detonator for rupturing the frangible end wall when it is desired to dispense the fluid.
To date there is no liquid dispensing system which is both reliable and ready to operate after standing idle for years, and at the same time is capable of delivering the pressurizing fluid at the high rate required to dispense the entire quantity of liquid contained for that purpose at a predetermined operating pressure. The systems described in the Fire Protection Manual require seals (such as valve seats and sealing rings) of non-metallic resilient material which will permit slow escape of gas, and which therefore require periodic checking to assure that the gas cylinders have sufficient pressure and that the system is ready to operate. The operating pressure would be considerably lower than the propellant storage pressure in the systems described in the Bayne, Morane et al. and Beckworth patents cited above, because the rate of heat transfer from the liquid to be dispensed to the propellant would be too slow to maintain the temperature and pressure of the propellant as it evaporates. There is needed a liquid dispensing system which has assured reliability after long standing, and which will reliably cause pressurization of the container of liquid to be dispensed, without substantial decrease of pressure during dispensing.